sfm at manduca.neurobio.arizona.edu (Stephen Matheson) writes:
>From article <3ris4k$65i at eldborg.rhi.hi.is>,
>by thoreys at rhi.hi.is (Thor Eysteinsson):
>>DvorakH at starbase1.caltech.edu (Hannah Dvorak) writes:
>>>In article <8AB22AA.0E53000E32.uuout at dkb.dk>, lars.thomsen at dkb.dk (LARS
>>>THOMSEN) wrote:
>>>> I was wondering if any one remembered good examples of
>>>> sensory neurones with the cell bodies close to the
>>>> location of the stimulus.
>>>Sure - photoreceptors.
>> I would say that nocireceptors (Pacinian corpuscles, Merkels disks,
>> etc.) were close to the stimulus,
>They are indeed, but they are not neurons. As I seem to
>recall, these receptors are composed modified connective-tissue cells,
>and are *innervated* by sensory neurons with distant cell bodies.
>The generator potential occurs in the dendrite(s) of the sensory
>neuron.
They are not "innervated" by sensory neurons, they are endings of
neurons ("dendritic"-like terminations).
>Similarly, gustatory cells in taste buds are made of modified
>epithelial cells (I think), and again are innervated by cranial
>sensory neurons in somewhat distant ganglia.
This is not similar, gustatory cells are indeed cells, pacinian or
Meissner corpuscule are neuritic endings. But it's true that they are
innervated by somewhat "distant" sensory perikarya (in ganglia of the Vth,
IXth and Xth nerves).
To answer the initial question, there is no true sensory neurons (in
vertebrates) for which the perikaryon could be considered near - and
directly affected by - the stimulus. There is always a cellular
interface between stimulus and the sensory endings. The sensory neurons
which could the better be defined like that are the ones produced by
placodal differentiation, and not by neural crest differentiation (in
vertebrates again), i.e. vestibulo-cochlear, some gustatory, visual,
olfactives (as you see it's only the special sense organs sensory neurons).
>Steve Matheson Program in Neuroscience University of Arizona
>sfm at neurobio.arizona.edu
Jeff
--
Jean-Francois Pflieger "DINANZI A ME NON FUR COSE CREATE,
Universite de Montreal SE NON ETERNE ED IO ETERNA DURO:
Sciences Neurologiques LASCIATE OGNI SPERANZA, VOI CH'ENTRATE"
pfliegej at alize.ere.umontreal.ca (Dante, "l'Enfer, Chant III, vers 7 a 9)